NEW YORK — Walmart Stores Inc. had the worst sales start to a month in seven years as payroll tax increases hit shoppers already battling a slow economy, according to internal e-mails obtained by Bloomberg News.

‘‘In case you haven’t seen a sales report these days, February MTD sales are a total disaster,’’ Jerry Murray, Walmart’s vice president of finance and logistics, said in a Feb. 12 e-mail to other executives, referring to month-to-date sales. ‘‘The worst start to a month I have seen in my ~ 7 years with the company.’’